Vacuum Advance Can

[William C.]

My 67 L79 has a 436-2? vacuum advance can in the car. LIC calls for a 236 can. Can someone give me the specs on these cans.

[Joe L.]

Re: Vacuum Advance Can

My 67 L79 has a 436-2? vacuum advance can in the car. LIC calls for a 236 can. Can someone give me the specs on these cans.

William-----


Yes, the GM #1116236, aka Delco #D1316A, is the original vacuum control used for your application. Its specs are as follows:

3-5 inches vacuum to start plunger
16 maximum crankshaft degrees @ 6-8 inches of vacuum

I don't know what the "-2" refers to as a suffix to "436". However, the GM #1973436 vacuum control, aka Delco #D1306A, has the following specs:

7-9 inches of vacuum to start plunger
20.5 maximum crankshaft degrees @ 16-18 inches vacuum

As you can see, the above two vacuum controls have COMPLETELY different characteristics.

[Wayne M.]

Re: Vacuum Advance Can

I don't know what the "-2" refers to as a suffix to "436". However, the GM #1973436 vacuum control, aka Delco #D1306A, has the following specs:

... 20.5 maximum crankshaft degrees @ 16-18 inches vacuum....

Joe -- I think William means by the question mark that there's a second character after the "2" which he can't make out, and from the distr. adv. spec of 10 degrees, it's probably a zero, or a "1"., as the stampings were always in crank degrees, although the Delco specs were not.

[William C.]

Re: Vacuum Advance Can

Thats correct Wayne. Thanks guys for the info.

[Duke W.]

Re: Vacuum Advance Can

Although OE, the 236 is more aggressive than necessary, and the 436 is a complete mismatch because it takes more vacuum to pull to the limit than the L-79 makes at idle (about 14-15" @ 750-800), and it has too much advance.

The 436 was probably used with an emission controlled engine that had ported vacuum advance.

A B20 or B26 (0@6", 16 @ 12") is the best match according to the "Two-Inch Rule".

Lot's more info on this subject in the archives.

Duke

[Larry M.]

Re: Vacuum Advance Can

Thats correct Wayne. Thanks guys for the info.

You can buy the cans Duke mentioned through NAPA, AC Delco, and other auto parts houses. Cost is very low $. Exact part numbers are in the archives.....or we can supply if needed.

An exact repro #236 can is also available. The contact names and ordering info is also in the archives. Cost is higher $$. Let us know if you need help.

Based on problems others have had in the past with the LIC #236, I would advise against ordering for a DRIVER car. Cost is $$ and actual performance is questionable.

Larry

[William C.]

Re: Vacuum Advance Can

You can buy the cans Duke mentioned through NAPA, AC Delco, and other auto parts houses. Cost is very low $. Exact part numbers are in the archives.....or we can supply if needed.

An exact repro #236 can is also available. The contact names and ordering info is also in the archives. Cost is higher $$. Let us know if you need help.

Based on problems others have had in the past with the LIC #236, I would advise against ordering for a DRIVER car. Cost is $$ and actual performance is questionable.

Larry

Larry,
NAPA has a ECHVC1765 which is a B26. I was going to order a 236, but will take your advise and get the B26. Do you and Duke agree on a B26?
Thanks,
Bill

[Larry M.]

Re: Vacuum Advance Can

Larry,
NAPA has a ECHVC1765 which is a B26. I was going to order a 236, but will take your advise and get the B26. Do you and Duke agree on a B26?
Thanks,
Bill

That should be a good choice. I would still check it against specs after purchase. You can use a MIGHTY-VAC or vacuum gage to see when it starts to pull in and when it is all in. After installing on the car, you can check the degrees vacuum advance with a timing light.

However, it is probably fine without checking if you do not have the tools/equipment. Most folks never bother.

Larry

[William C.]

Re: Vacuum Advance Can

Larry,
Thanks for your help..Bill

[Duke W.]

Re: Vacuum Advance Can

A VC-1765 will either be a B20 or a B26. The latter was formerly VC-1808, but it's essentially the same specs at B20, so both were consolidated under the VC-1765 part number, and either is okay.

As previously advised, I suggest you check before leaving the store that maximum advance is achieved at about 12". Then you can check on the car to be sure that it yields about 16 degrees at idle.

Duke

[William C.]

Re: Vacuum Advance Can

A VC-1765 will either be a B20 or a B26. The latter was formerly VC-1808, but it's essentially the same specs at B20, so both were consolidated under the VC-1765 part number, and either is okay.

As previously advised, I suggest you check before leaving the store that maximum advance is achieved at about 12". Then you can check on the car to be sure that it yields about 16 degrees at idle.

Duke

Will do, Thanks Duke for you help..Bill

[Richard D.]

Re: Vacuum Advance Can

My 67 L79 has a 436-2? vacuum advance can in the car. LIC calls for a 236 can. Can someone give me the specs on these cans.

I had this on file when I had my distributor redone with the can specs by number and year. It seems to be very accurate. Hope this is useful to you. Rich

[Larry M.]

Re: Vacuum Advance Can

I had this on file when I had my distributor redone with the can specs by number and year. It seems to be very accurate. Hope this is useful to you. Rich

Rich:

Thanks for the information. Lars (always) has excellent, accurate, and easy-to-follow instructions. This should benefit many. I put a copy in my files for the future.

Larry

[Duke W.]

Re: Vacuum Advance Can

That's an old, obsolete version of Lars' paper. The latest version has a revised application list that we developed together and additional explanatory information (written by me) on what makes a suitable spark advance map for a particular engine configuration and why. The latest version is here:

http://www.lbfun.com/warehouse/tech_...ance_Specs.pdf

For example, we eliminated the B1 applications such as base cam Corvette engines because it's really not the best choice, but is based on some ill-conceived parts substitutions done by GM long after our cars were built.

There are three VACs that meet the needs of any OE Corvette engine with full time vacuum advance or ported advance engines that are converted to full time. All are based on applying the "Two-Inch Rule" to typical idle vacuum and are the first three listings in the latest revision.

15", B22 - all base engines/optional engines that use the base engine camshaft (283-220/230/245/250/275HP; 327-250/300HP) with manual trans

12", B20 or B26 - all big blocks, all base engines/optional engines that use the base engine camshaft (as above) with auto trans, L-79, L-46; L-82 w/ MT.

8", B28 all mechanical lifter cam small blocks; L-82 w/ AT.

One application I'm not sure about is big blocks with auto trans, since I've never gotten a reliable report on their manifold vacuum/idle speed idling in Drive. If they pull less than about 13-14" they should use a B28.

[Larry M.]

Re: Vacuum Advance Can

Duke:

Thanks for the update.......this newest one is even better. I much appreciate it.

Larry